This invention relates to a hydraulic needle bar positioning apparatus for a multiple needle tufting machine, and more particularly to a computer control system for a hydraulic needle bar positioning apparatus for a multiple needle tufting machine.
Heretofore in the production of tufted fabrics, distinctive patterns, such as various zig-zag patterns have been formed in backing fabrics by transversely or laterally shifting the needle bar, or by shifting the backing material support beneath the needles, needle-gauge increments for each stitch, in accordance with a predetermined pattern.
One means for executing this lateral or transverse shifting of the needle bar, or the backing material support, is a pattern cam continuously rotated in synchronism with the rotary drive of the tufting machine, in which the pattern cam engages a movable needle bar, or a laterally reciprocably movable backing material support. Examples of such pattern cam control mechanisms for laterally shiftable needle bars or fabric supports are disclosed in numerous prior U.S. patents, such as the following:
______________________________________ 2,513,261 Behrens June 27, 1950 2,679,218 Jones May 25, 1954 2,682,841 McCutchen July 6, 1954 2,855,879 Manning et al Oct. 14, 1958 3,026,830 Bryant et al Mar. 27, 1962 3,100,465 Broaderick Aug. 13, 1963 3,109,395 Batty et al Nov. 5, 1963 3,396,687 Nowicki Aug. 13, 1968 ______________________________________
There are numerous disadvantages in the use of pattern cams for controlling the lateral or transverse shifting of needle bars or fabric supports.
Since the pattern cam control mechanism is entirely mechanical, there is considerable wear on both the cam surfaces and the cam rollers or followers.
There is a long change-over period for the pattern cams, when patterns of different designs are required.
Machine speed is limited by, not only the mechanical arrangement, but also the abrupt changes in the pattern cam surfaces.
There is extremely high machine stress caused by having no accelerate the lateral movement of the needle bar to near infinity because of the sharp cam lobes.
Where there are machining inaccuracies in the profile of the cams, differing lateral or transverse relationships between the hooks and needles may be produced for different pattern positions.
The continuous operation of the pattern cams and cam followers produces an excessive noise level.
The common assignee's prior U.S. Pat. No. 4,173,192 discloses an electrohydraulic needle bar positioning apparatus including a hydraulic actuator coupled to the needle bar and controlled by an electronic control circuit including a PROM (Programmable Read Only Memory) for deter mining the stitch pattern of the tufting machine.
Although the electrohydraulic needle bar positioner of the prior U.S. Pat. No. 4,173,192, overcame many of the disadvantages of a cam-controlled needle bar positioner or shifter, nevertheless, the electronic controls for the previous electrohydraulic needle bar positioner produced an instantaneous command change to the hydraulic actuator calling for instantaneous maximum speed of the transversely moving needle bar independent of the tufting machine's main motor speed. Such abrupt speed changes caused excessive shock loads to the machinery which in turn limited the machine life.